Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

But experts say there's little evidence that extreme regimens such as the Master Cleanse or Fruit Flush do anything more than lead to unpleasant, unhealthy side effects.

Still, these super-restrictive eating plans are hotter than ever, thanks to being linked to lanky celebrities including Gwyneth Paltrow and Angelina Jolie. Beyonce Knowles attributed her 20-pound weight loss for the movie "Dreamgirls" to the Master Cleanse — a starvation diet whose adherents swallow nothing but a concoction of lemon juice mixed with maple syrup, water and cayenne pepper, as well as salt water and a laxative tea for 10 days.

The idea of detoxifying or purifying the body of harmful substances has been around for centuries and cycles back into popularity now and again. There are nohard numbers on how many people have tried the latest fashionable plans, much less stuck with them, but dozens of new do-it-yourself fasting books are glutting bookstore shelves.

That's what has nutrition experts sounding the alarm over possible risks from lengthy or repeated fasts. Vitamin deficiencies, muscle breakdown and blood-sugar problems — not to mention frequent liquid bowel movements — are some of the seriously unpleasant drawbacks to these plans, which are skimpy on solid foods and often call for laxatives.

“Long-term fasts lead to muscle breakdown and a shortage of many needed nutrients,” says Lona Sandon, a Dallas dietitian and spokesperson for the American Dietetic Association. Depriving the body of the vitamins and minerals we get fromfood can "actually weaken the body’s ability to fight infections and inflammation,” she says.

Because the crash diets can upset blood sugar, potassium and sodium levels in the body, people with diabetes, heart or kidney disease or women who are pregnant or nursing shouldn't try them, experts say. Children, teens, older adults or people with certain digestive conditions should also steer clear.

The scores of detox diet books and kits out there each have their own take on how to cleanse the body — one calls for spices and fruit juices, another for only vegetable purees — but most of them boil down to extremely low-calorie, primarily liquid diets.

The idea behind these plans, which can last anywhere from three days to about a month,is to rid the body of toxins absorbed from the environment and the less-than-healthy foods we eat. This cleansing is supposed to leave you feeling energized.

Some plans restrict all solid foods and instruct dieters to survive on only low-calorie beverages for days at a time. The Joshi holistic diet involves an elaborate list of so-called acid-forming foods to avoid for three weeks, including seemingly healthy veggies and grains.

“Your body does a perfectly good job of getting rid of toxins on its own,” says Dr. Nasir Moloo, a gastroenterologist with Capitol Gastroenterology Consultants Medical Group in Sacramento, Calif. “There’s no evidence that these types of diets are necessary or helpful.”

While there are medical conditions that interfere with organ function and prevent the body from clearing toxins, healthy people already have a built-in detoxification system — the liver, kidneys, lungs and skin, says Moloo.

And by attempting to flush out the “bad stuff” from our intestines, Sandon warns, you're also "flushing out the good bacteria that keep the intestines healthy.”

Lots of bathroom time
The side effects from prolonged, severe calorie restriction can include headache, fatigue, irritability, aches and pains. Because many rely on aggressive laxatives, these diets can also get pretty messy. Frequent bathroom visits can lead to irritation and breakdown of skin on your bottom, as well as dehydration.
Video: Do detox diets really work?

While believers claim they feel lighter and more energetic, studies on starvation show the longer you fast, the more lethargic and less focused you become. Because most of these diets contain very little protein, it can be difficult for the body to rebuild lost muscle tissue.

Although people can quickly drop pounds on these diets, the majority of people regain all the weight they lose on any diet, especially the highly restrictive varieties, according to recent research published in American Psychologist, the journal of the American Psychological Association. While people can lose 5 to 10 percent of their weight in the first few months of a diet, up to two-thirds of people regain even more weight than they lost within four or five years, the researchers found.

Cutting back on high-fat foods, eating in moderation and consuming more vegetables and fruits may not seem as glamorous as starving yourself like a celebrity for days, but it's healthier for you in the long run and certainly sexier than rushing to the bathroom all day.

Susan Moores, R.D., is a nutrition consultant and spokesperson for The American Dietetic Association.